Fucosylated chondroitin sulfate inhibits Plasmodium falciparum cytoadhesion and merozoite invasion

NANOPARTICLE-BASED formulation of dihydroartemisinin-lumefantrine duo-drugs: Preclinical Evaluation and enhanced antimalarial efficacy in a mouse model

Artemisinin-based combinations (ACTs) are World Health Organization-recommended treatment for malaria. Artemether (A) and lumefantrine (LUM) were the first co-formulated ACT and first-line treatment for malaria globally, artemether is dihydroartemisinin's (DHA's) prodrug. Artemisinins and LUM face low aqueous solubility while artemisinin has low bioavailability and short half-life thus requiring continuous dosage to maintain adequate therapeutic drug-plasma concentration. This study aimed at improving ACTs limitations by nano-formulating DHA-LUM using solid lipid nanoparticles (SLNs) as nanocarrier. SLNs were prepared by modified solvent extraction method based on water-in-oil-in-water double emulsion. Mean particle size, polydispersity index and zeta potential were 308.4 nm, 0.29 and -16.0 mV respectively. Nanoencapsulation efficiencies and drug loading of DHA and LUM were 93.9%, 33.7%, 11.9%, and 24.10% respectively. Nanoparticles were spherically shaped and drugs followed Kors-Peppas release model, steadily released for over 72 h. DHA-LUM-SLNs were 31% more efficacious than conventional oral doses in clearing Plasmodium berghei from infected Swiss albino mice.

Red Blood Cells Oligosaccharides as Targets for Plasmodium Invasion

The key element in developing a successful malaria treatment is a good understanding of molecular mechanisms engaged in human host infection. It is assumed that oligosaccharides play a significant role in Plasmodium parasites binding to RBCs at different steps of host infection. The formation of a tight junction between EBL merozoite ligands and glycophorin receptors is the crucial interaction in ensuring merozoite entry into RBCs. It was proposed that sialic acid residues of O/N-linked glycans form clusters on a human glycophorins polypeptide chain, which facilitates the binding. Therefore, specific carbohydrate drugs have been suggested as possible malaria treatments. It was shown that the sugar moieties of N-acetylneuraminyl-N-acetate-lactosamine and 2,3-didehydro-2-deoxy-N-acetylneuraminic acid (DANA), which is its structural analog, can inhibit P. falciparum EBA-175-GPA interaction. Moreover, heparin-like molecules might be used as antimalarial drugs with some modifications to overcome their anticoagulant properties. Assuming that the principal interactions of Plasmodium merozoites and host cells are mediated by carbohydrates or glycan moieties, glycobiology-based approaches may lead to new malaria therapeutic targets.

3D Organoid Assay of the Impact of Infected Erythrocyte Adhesion on the Blood-Brain Barrier

Mass sequestration of Plasmodium falciparum parasites in the brain microvasculature can lead to cerebral malaria (CM), characterized by inflammation, vessel occlusion, and brain swelling. To date, only single-cell-type, monolayer assays have been used to investigate the effect of infected erythrocytes (IEs) on the human blood-brain barrier (BBB) and the underlying parenchyma. Here we present a human-derived 3D model of the BBB comprised of endothelial cells, pericytes, and astrocytes in direct contact with each other. The organoids readily self-assemble and can easily be grown in 96-well plates, allowing for high-throughput analysis. These organoids allow for the assessment of parasite adhesion, and analysis of barrier function, and gross morphological changes in response to parasite exposure.

Measuring Rosetting Inhibition in Plasmodium falciparum Parasites Using a Flow Cytometry-Based Assay

Rosetting is the ability of Plasmodium falciparum-infected erythrocytes (IEs) to bind to host receptors on the surface of uninfected erythrocytes (uE) leading to the formation of a cluster of cells with a central IE surrounded by uE. It is a hallmark event during the pathogenesis of P. falciparum malaria, the most severe species causing malaria, which affects mostly young children in Africa. There are no current treatments effectively targeting and disrupting parasite rosette formation. Here, we detail a high-throughput, flow cytometry based assay that allows testing and identification of potential rosetting-inhibitory compounds that could be used in combination with anti-plasmodial drugs to reduce malaria morbidity and mortality.

Antiparasitic Effects of Sulfated Polysaccharides from Marine Hydrobionts

This review presents materials characterizing sulfated polysaccharides (SPS) of marine hydrobionts (algae and invertebrates) as potential means for the prevention and treatment of protozoa and helminthiasis. The authors have summarized the literature on the pathogenetic targets of protozoa on the host cells and on the antiparasitic potential of polysaccharides from red, brown and green algae as well as certain marine invertebrates. Information about the mechanisms of action of these unique compounds in diseases caused by protozoa has also been summarized. SPS is distinguished by high antiparasitic activity, good solubility and an almost complete absence of toxicity. In the long term, this allows for the consideration of these compounds as effective and attractive candidates on which to base drugs, biologically active food additives and functional food products with antiparasitic activity.

Unveiling the Sugary Secrets of Plasmodium Parasites

Plasmodium parasites cause malaria disease, one of the leading global health burdens for humanity, infecting hundreds of millions of people each year. Different glycans on the parasite and the host cell surface play significant roles in both malaria pathogenesis and host defense mechanisms. So far, only small, truncated N- and O-glycans have been identified in Plasmodium species. In contrast, complex glycosylphosphatidylinositol (GPI) glycolipids are highly abundant on the parasite’s cell membrane and are essential for its survival. Moreover, the parasites express lectins that bind and exploit the host cell surface glycans for different aspects of the parasite life cycle, such as adherence, invasion, and evasion of the host immune system. In parallel, the host cell glycocalyx and lectin expression serve as the first line of defense against Plasmodium parasites and directly dictate susceptibility to Plasmodium infection. This review provides an overview of the glycobiology involved in Plasmodium-host interactions and its contribution to malaria pathogenesis. Recent findings are presented and evaluated in the context of potential therapeutic exploitation.

Biocompatibility and structural characterization of glycosaminoglycans isolated from heads of silver-banded whiting (Sillago argentifasciata Martin & Montalban 1935)

Glycosaminoglycans (GAGs) were extracted from heads of silver-banded whiting (SBW) fish and subjected to preliminary biocompatibility testing per ISO 10993: intracutaneous irritation, maximization sensitization, systemic toxicity, and cytotoxicity. When the GAG solution was injected intradermally, the observed irritation was within ISO limits and comparable to a marketed control. There was no evidence of sensitization, systemic toxicity, or cellular toxicity on the test organisms treated with the GAG mixture from SBW fish heads. Fractionation by size-exclusion chromatography has shown three distinct fractions: F1 as low molecular weight hyaluronic acid (190 kDa), F2 (82 kDa) and F3 (64 kDa), both as chondroitin sulfates. Structural characterization by 1D and 2D nuclear magnetic resonance spectroscopy and disaccharide analysis have shown sulfation ratios at positions C4:C6 of the F2 and F3 fractions respectively as 70:20% and 50:30%, and the balance of non-sulfated and 4,6-di-sulfated units. The preliminary results here suggest that GAG-based extracts from SBW fish heads are suitable alternative products to be used in soft tissue augmentation, although further long-term biocompatibility studies are still required.

Galactosaminoglycans: Medical Applications and Drawbacks

Galactosaminoglycans (GalAGs) are sulfated glycans composed of alternating N-acetylgalactosamine and uronic acid units. Uronic acid epimerization, sulfation patterns and fucosylation are modifications observed on these molecules. GalAGs have been extensively studied and exploited because of their multiple biomedical functions. Chondroitin sulfates (CSs), the main representative family of GalAGs, have been used in alternative therapy of joint pain/inflammation and osteoarthritis. The relatively novel fucosylated chondroitin sulfate (FCS), commonly found in sea cucumbers, has been screened in multiple systems in addition to its widely studied anticoagulant action. Biomedical properties of GalAGs are directly dependent on the sugar composition, presence or lack of fucose branches, as well as sulfation patterns. Although research interest in GalAGs has increased considerably over the three last decades, perhaps motivated by the parallel progress of glycomics, serious questions concerning the effectiveness and potential side effects of GalAGs have recently been raised. Doubts have centered particularly on the beneficial functions of CS-based therapeutic supplements and the potential harmful effects of FCS as similarly observed for oversulfated chondroitin sulfate, as a contaminant of heparin. Unexpected components were also detected in CS-based pharmaceutical preparations. This review therefore aims to offer a discussion on (1) the current and potential therapeutic applications of GalAGs, including those of unique features extracted from marine sources, and (2) the potential drawbacks of this class of molecules when applied to medicine.

Targeting malaria parasite invasion of red blood cells as an antimalarial strategy

Plasmodium spp. parasites that cause malaria disease remain a significant global-health burden. With the spread of parasites resistant to artemisinin combination therapies in Southeast Asia, there is a growing need to develop new antimalarials with novel targets. Invasion of the red blood cell by Plasmodium merozoites is essential for parasite survival and proliferation, thus representing an attractive target for therapeutic development. Red blood cell invasion requires a co-ordinated series of protein/protein interactions, protease cleavage events, intracellular signals, organelle release and engagement of an actin-myosin motor, which provide many potential targets for drug development. As these steps occur in the bloodstream, they are directly susceptible and exposed to drugs. A number of invasion inhibitors against a diverse range of parasite proteins involved in these different processes of invasion have been identified, with several showing potential to be optimised for improved drug-like properties. In this review, we discuss red blood cell invasion as a drug target and highlight a number of approaches for developing antimalarials with invasion inhibitory activity to use in future combination therapies.

A new heparan sulfate from the mollusk Nodipecten nodosus inhibits merozoite invasion and disrupts rosetting and cytoadherence of Plasmodium falciparum

BACKGROUND

Despite treatment with effective antimalarial drugs, the mortality rate is still high in severe cases of the disease, highlighting the need to find adjunct therapies that can inhibit the adhesion of Plasmodium falciparum-infected erythrocytes (Pf-iEs).

OBJECTIVES

In this context, we evaluated a new heparan sulfate (HS) from Nodipecten nodosus for antimalarial activity and inhibition of P. falciparum cytoadhesion and rosetting.

METHODS

Parasite inhibition was measured by SYBR green using a cytometer. HS was assessed in rosetting and cytoadhesion assays under static and flow conditions using Chinese hamster ovary (CHO) and human lymphatic endothelial cell (HLEC) cells expressing intercellular adhesion molecule-1 (ICAM1) and chondroitin sulfate A (CSA), respectively.

FINDINGS

This HS inhibited merozoite invasion similar to heparin. Moreover, mollusk HS decreased cytoadherence of P. falciparum to CSA and ICAM-1 on the surface of endothelial cells under static and flow conditions. In addition, this glycan efficiently disrupted rosettes.

CONCLUSIONS

These findings support a potential use for mollusk HS as adjunct therapy for severe malaria.

A Glycosaminoglycan Extract from Portunus pelagicus Inhibits BACE1, the β Secretase Implicated in Alzheimer's Disease

Therapeutic options for Alzheimer's disease, the most common form of dementia, are currently restricted to palliative treatments. The glycosaminoglycan heparin, widely used as a clinical anticoagulant, has previously been shown to inhibit the Alzheimer's disease-relevant β-secretase 1 (BACE1). Despite this, the deployment of pharmaceutical heparin for the treatment of Alzheimer's disease is largely precluded by its potent anticoagulant activity. Furthermore, ongoing concerns regarding the use of mammalian-sourced heparins, primarily due to prion diseases and religious beliefs hinder the deployment of alternative heparin-based therapeutics. A marine-derived, heparan sulphate-containing glycosaminoglycan extract, isolated from the crab Portunus pelagicus, was identified to inhibit human BACE1 with comparable bioactivity to that of mammalian heparin (IC50 = 1.85 μg mL-1 (R2 = 0.94) and 2.43 μg mL-1 (R2 = 0.93), respectively), while possessing highly attenuated anticoagulant activities. The results from several structural techniques suggest that the interactions between BACE1 and the extract from P. pelagicus are complex and distinct from those of heparin.

Polyamidoamine Nanoparticles for the Oral Administration of Antimalarial Drugs

Current strategies for the mass administration of antimalarial drugs demand oral formulations to target the asexual Plasmodium stages in the peripheral bloodstream, whereas recommendations for future interventions stress the importance of also targeting the transmission stages of the parasite as it passes between humans and mosquitoes. Orally administered polyamidoamine (PAA) nanoparticles conjugated to chloroquine reached the blood circulation and cured Plasmodium yoelii-infected mice, slightly improving the activity of the free drug and inducing in the animals immunity against malaria. Liquid chromatography with tandem mass spectrometry analysis of affinity chromatography-purified PAA ligands suggested a high adhesiveness of PAAs to Plasmodium falciparum proteins, which might be the mechanism responsible for the preferential binding of PAAs to Plasmodium-infected erythrocytes vs. non-infected red blood cells. The weak antimalarial activity of some PAAs was found to operate through inhibition of parasite invasion, whereas the observed polymer intake by macrophages indicated a potential of PAAs for the treatment of certain coinfections such as Plasmodium and Leishmania. When fluorescein-labeled PAAs were fed to females of the malaria mosquito vectors Anopheles atroparvus and Anopheles gambiae, persistent fluorescence was observed in the midgut and in other insect's tissues. These results present PAAs as a versatile platform for the encapsulation of orally administered antimalarial drugs and for direct administration of antimalarials to mosquitoes, targeting mosquito stages of Plasmodium.

Therapeutic strategies to target microbial protein-glycosaminoglycan interactions

Glycans are involved in a plethora of human pathologies including infectious diseases. Especially, glycosaminoglycans (GAGs), like heparan sulfate and chondroitin sulfate, have been found to be involved in different crucial stages of microbial invasion. Here, we review various therapeutic approaches, which target the interface of host GAGs and microbial proteins and discuss their limitations and challenges for drug development.

Marine glycosaminoglycan-like carbohydrates as potential drug candidates for infectious disease

Glycosaminoglycans (GAGs), present in the extracellular matrix, are exploited by numerous, distinct microbes for cellular attachment, adhesion, invasion and evasion of the host immune system. Glycosaminoglycans, including the widely used, clinical anticoagulant heparin and semi-synthetic analogues thereof, have been reported to inhibit and disrupt interactions between microbial proteins and carbohydrates present on the surface of host cells. However, the anticoagulant properties of unmodified, pharmaceutical heparin preparations preclude their capabilities as therapeutics for infectious disease states. Here, unique Glycosaminoglycan-like saccharides from various, distinct marine species are reported for their potential use as therapeutics against infectious diseases; many of which possess highly attenuated anticoagulant activities, while retaining significant antimicrobial properties.

Pharmacological Potential of Sea Cucumbers

This review presents a detailed analysis of published research data focused on the pharmacological activity exerted by biologically active compounds isolated from sea cucumbers belonging to the class of Holothuroidea, phylum Echinodermata. The review contains descriptions of the structure, physico-chemical properties and pharmacological effects of these active substances. Particular attention is given to compounds with anticoagulant, antithrombotic, antioxidant, anticancer, anti-infectious, immune-stimulating and anti-ACE (angiotensin converting enzyme) activities as well as to the substances exerting a regulating influence on lipid and carbohydrate metabolism. All these compounds may be considered as prototypes for development of new pharmaceutical substances and medicines.

Identification of Heparin Modifications and Polysaccharide Inhibitors of Plasmodium falciparum Merozoite Invasion That Have Potential for Novel Drug Development

Despite recent successful control efforts, malaria remains a leading global health burden. Alarmingly, resistance to current antimalarials is increasing and the development of new drug families is needed to maintain malaria control. Current antimalarials target the intraerythrocytic developmental stage of the Plasmodium falciparum life cycle. However, the invasive extracellular parasite form, the merozoite, is also an attractive target for drug development. We have previously demonstrated that heparin-like molecules, including those with low molecular weights and low anticoagulant activities, are potent and specific inhibitors of merozoite invasion and blood-stage replication. Here we tested a large panel of heparin-like molecules and sulfated polysaccharides together with various modified chemical forms for their inhibitory activity against P. falciparum merozoite invasion. We identified chemical modifications that improve inhibitory activity and identified several additional sulfated polysaccharides with strong inhibitory activity. These studies have important implications for the further development of heparin-like molecules as antimalarial drugs and for understanding merozoite invasion.

Heparin: new life for an old drug

Heparin is one of the oldest drugs, which nevertheless remains in widespread clinical use as an inhibitor of blood coagulation. The history of its identification a century ago unfolded amid one of the most fascinating scientific controversies turning around the distribution of credit for its discovery. The composition, purification and structure-function relationship of this naturally occurring glycosaminoglycan regarding its classical role as anticoagulant will be dealt with before proceeding to discuss its therapeutic potential in, among other, inflammatory and infectious disease, cancer treatment, cystic fibrosis and Alzheimer's disease. The first bibliographic reference hit using the words 'nanomedicine' and 'heparin' is as recent as 2008. Since then, nanomedical applications of heparin have experienced an exponential growth that will be discussed in detail, with particular emphasis on its antimalarial activity. Some of the most intriguing potential applications of heparin nanomedicines will be exposed, such as those contemplating the delivery of drugs to the mosquito stages of malaria parasites.

New Applications of Heparin and Other Glycosaminoglycans

Heparin, the widely used pharmaceutical anticoagulant, has been in clinical use for well over half a century. Its introduction reduced clotting risks substantially and subsequent developments, including the introduction of low-molecular-weight heparin, made possible many major surgical interventions that today make heparin an indispensable drug. There has been a recent burgeoning of interest in heparin and related glycosaminoglycan (GAG) polysaccharides, such as chondroitin sulfates, heparan sulfate, and hyaluronate, as potential agents in various applications. This ability arises mainly from the ability of GAGs to interact with, and alter the activity of, a wide range of proteins. Here, we review new developments (since 2010) in the application of heparin and related GAGs across diverse fields ranging from thrombosis and neurodegenerative disorders to microbiology and biotechnology.

Marine organism sulfated polysaccharides exhibiting significant antimalarial activity and inhibition of red blood cell invasion by Plasmodium

The antimalarial activity of heparin, against which there are no resistances known, has not been therapeutically exploited due to its potent anticoagulating activity. Here, we have explored the antiplasmodial capacity of heparin-like sulfated polysaccharides from the sea cucumbers Ludwigothurea grisea and Isostichopus badionotus, from the red alga Botryocladia occidentalis, and from the marine sponge Desmapsamma anchorata. In vitro experiments demonstrated for most compounds significant inhibition of Plasmodium falciparum growth at low-anticoagulant concentrations. This activity was found to operate through inhibition of erythrocyte invasion by Plasmodium, likely mediated by a coating of the parasite similar to that observed for heparin. In vivo four-day suppressive tests showed that several of the sulfated polysaccharides improved the survival of Plasmodium yoelii-infected mice. In one animal treated with I. badionotus fucan parasitemia was reduced from 10.4% to undetectable levels, and Western blot analysis revealed the presence of antibodies against P. yoelii antigens in its plasma. The retarded invasion mediated by sulfated polysaccharides, and the ensuing prolonged exposure of Plasmodium to the immune system, can be explored for the design of new therapeutic approaches against malaria where heparin-related polysaccharides of low anticoagulating activity could play a dual role as drugs and as potentiators of immune responses.

Surface Proteoglycans as Mediators in Bacterial Pathogens Infections

Infectious diseases remain an important global health problem. The interaction of a wide range of pathogen bacteria with host cells from many different tissues is frequently mediated by proteoglycans. These compounds are ubiquitous complex molecules which are not only involved in adherence and colonization, but can also participate in other steps of pathogenesis. To overcome the problem of microbial resistance to antibiotics new therapeutic agents could be developed based on the characteristics of the interaction of pathogens with proteoglycans.

The influence of host genetics on erythrocytes and malaria infection: is there therapeutic potential?

As parasites, Plasmodium species depend upon their host for survival. During the blood stage of their life-cycle parasites invade and reside within erythrocytes, commandeering host proteins and resources towards their own ends, and dramatically transforming the host cell. Parasites aptly avoid immune detection by minimizing the exposure of parasite proteins and removing themselves from circulation through cytoadherence. Erythrocytic disorders brought on by host genetic mutations can interfere with one or more of these processes, thereby providing a measure of protection against malaria to the host. This review summarizes recent findings regarding the mechanistic aspects of this protection, as mediated through the parasites interaction with abnormal erythrocytes. These novel findings include the reliance of the parasite on the host enzyme ferrochelatase, and the discovery of basigin and CD55 as obligate erythrocyte receptors for parasite invasion. The elucidation of these naturally occurring malaria resistance mechanisms is increasing the understanding of the host-parasite interaction, and as discussed below, is providing new insights into the development of therapies to prevent this disease.

Gellan sulfate inhibits Plasmodium falciparum growth and invasion of red blood cells in vitro

Here, we assessed the sulfated derivative of the microbial polysaccharide gellan gum and derivatives of λ and κ-carrageenans for their ability to inhibit Plasmodium falciparum 3D7 and Dd2 growth and invasion of red blood cells in vitro. Growth inhibition was assessed by means of flow cytometry after a 96-h exposure to the inhibitors and invasion inhibition was assessed by counting ring parasites after a 20-h exposure to them. Gellan sulfate strongly inhibited invasion and modestly inhibited growth for both P. falciparum 3D7 and Dd2; both inhibitory effects exceeded those achieved with native gellan gum. The hydrolyzed λ-carrageenan and oversulfated κ-carrageenan were less inhibitory than their native forms. In vitro cytotoxicity and anticoagulation assays performed to determine the suitability of the modified polysaccharides for in vivo studies showed that our synthesized gellan sulfate had low cytotoxicity and anticoagulant activity.